The UK secretary of state for the environment, food and rural affairs says the challenge for the UN Earth summit must be how to 'green' the world economy

Sustainable agriculture should be the UK's key objective for Rio+20, according to the UK secretary of state for the environment, food and rural affairs, Caroline Spelman, who will be attending next month's UN conference on sustainable development with the deputy prime minister Nick Clegg.

"Everywhere in the world, wherever farmers farm, should be put on a sustainable footing," she told a Faith in Rio debate in London on Wednesday, organised by the NGOs Cafod, Christian Aid, Tearfund and Progressio. "Just imagine if we could move farmers from subsistence to sustainability," she added, citing some farmers' inability to store produce and water as an example of where low-key technology could make a real difference in developing countries.

Spelman gave her support to the creation of a set of sustainable development goals, which have been suggested both as an aim for Rio+20 and to inform the debate on objectives for development post-2015, when the millennium development goals, which Spelman described as "a very good model of how to drive action forward", expire. She said the UK delegation "want to come away [from Rio] with a statement of intent and a plan of action".

Outlining the challenges facing policymakers in Rio, and perhaps the failures of the UN Earth summit 20 years ago, which, for the first time sought to address concerns about environmental protection and social and economic development, Spelman claimed that "the poorest 20 years ago are still the poorest today", and warned that "sustainability is not fully integrated into economic decision-making. The world's economy needs to be greened. A green economy can't be a subset."

Water, land and energy should form the nexus of the SDGs, Spelman said, echoing the sentiments of the European Development Report published last week. She called for a small number of goals focused on the most critical sustainability issues. She added: "SDGs have to be relevant to individuals and meaningful at a local level. It isn't all about carbon. The worthy and wordy zero document [the draft outcome document for Rio+20] is not going to save the planet; 400 paragraphs is not the answer."

But Peter Price, the bishop of Bath and Wells, warned the debate that the SDGs would be "voluntary" and "aspirational" with "not very much legal pressure" to bring them into force.

Despite concerns that the non-committal attitude of the US president Barack Obama to Rio+20 will prevent any meaningful outcomes for the summit, Spelman said there was "recognition by superpowers that power is on the move. The distinction between developed and developing has begun to slip away. The economic crash has not distracted from our will to make progress on sustainable development."

She said she was "encouraged" by the attitudes of China, Brazil, India and Russia to put growth on a sustainable footing, citing China and India's desire for a water sustainability goal to emerge from Rio to avoid conflict over water resources, particularly in the Himalayas.

Spelman encouraged the business community to put sustainability at the heart of their decision-making and drive a green economy, saying: "Companies are asking for governance. Companies have a very good reason to put sustainability at the heart of their operations – to show, above all, that business wants this … after the disastrous consequences of unsustainable growth. The exciting thing is that businesses want to do this."

Her view was echoed by UK insurer Aviva's chief responsible investment officer Steve Waygood, whose company is asking world leaders at Rio+20 to commit to a convention on sustainable reporting, claiming that the Brazil gathering will be the first time corporate social responsibility has been discussed at a global summit since the 1992 summit's declaration on CSR, which lasted only two years.

Waygood called on companies to "embed sustainability in their disclosures to the market". The Rio+20 zero draft document calls for greater corporate responsibility, and Aviva – in coalition with NGOs, the FTSE, investment management companies and others is calling for a "report or explain" standard for companies to declare their sustainable business practices to allow consumers and investors, whether large corporate investors or individuals with pension funds, to make informed decisions about how their money is used.

"If we want responsible capitalism … so that the right companies are getting the capital, there is a massive data gap," he said. He called on Rio+20 to deliver a mechanism to require large and listed companies to declare their thinking on sustainability, and, if they have done nothing, to explain why not. "We need a regulatory or policy vehicle to prevent us having the same conversation with different companies," he added.